A vehicle may contain automatic safety restraint actuators that are activated responsive to a vehicle crash for purposes of mitigating occupant injury. Examples of such automatic safety restraint actuators include air bags, seat belt pretensioners, and deployable knee bolsters. One objective of an automatic restraint system is to mitigate occupant injury, thereby not causing more injury with the automatic restraint system than would be caused by the crash had the automatic restraint system not been activated. Generally, it is desirable to only activate automatic safety restraint actuators when needed to mitigate injury because of the expense of replacing the associated components of the safety restraint system, and because of the potential for such activations to harm occupants. This is particularly true of air bag restraint systems, wherein occupants too close to the air bag at the time of deployment--i.e. out-of-position occupants--are vulnerable to injury or death from the deploying air bag even when the associated vehicle crash is relatively mild. Moreover, occupants who are of small stature or with weak constitution, such as children, small adults or people with frail bones are particularly vulnerable to injury induced by the air bag inflator. Furthermore, infants properly secured in a normally positioned rear facing infant seat (RFIS) in proximity to a front seat passenger-side air bag are also vulnerable to injury or death from the deploying air bag because of the close proximity of the infant seat's rear surface to the air bag inflator module.
Air bag inflators are designed with a given restraint capacity, as for example, the capacity to protect an unbelted normally seated fiftieth percentile occupant when subjected to a 30 MPH barrier equivalent crash, which results in associated energy and power levels which can be injurious to out-of-position occupants. While relatively infrequent, cases of injury or death caused by air bag inflators in crashes for which the occupants would have otherwise survived relatively unharmed have provided the impetus to reduce or eliminate the potential for air bag inflators to injure the occupants which they are intended to protect.
Known deployment systems for vehicle safety devices such as an air bag require the host vehicle to actually collide with an obstacle or other vehicle before the deployment decision process begins. At that point in time, the sensors detect a deceleration in the host vehicle and deploy one or more safety systems. Thus, the crash is identified based solely on the characteristic of the acceleration versus time measure. The disadvantage with existing post-crash detection systems derives from the fact that the time available to deploy an active safety device is very short, particularly for side impact or high speed frontal collisions where occupant restraint systems can provide significant safety benefits. These short time frames lead to rates of inflation of the airbags that are so great that injury or death are possible if the occupant is not well aligned with the airbag.
One technique for mitigating injury by the air bag inflator to occupants is to reduce the power and energy levels of the associated air bag inflator, for example by reducing the amount of gas generant in the air bag inflator, or the inflation rate thereof. This reduces the risk of harm to occupants by the air bag inflator while simultaneously reducing the restraint capacity of the air bag inflator, which places occupants at greater risk for injury when exposed to higher severity crashes.
Another technique for mitigating injury by the air bag inflator to occupants is to control the rate of inflation rate or the capacity of the inflator responsive to a measure of the severity of the crash. The prior art teaches the use of multi-stage inflators having distinct independent compartmentalized stages and corresponding firing circuits, whereby the stages may be fired in delayed succession to control the effective inflation rate, or stages may be inhibited from firing to control the effective inflator capacity. The prior art also teaches the use of a hybrid inflator having a combination of stored gas and plural pyrotechnic gas generator elements which are independently fired. Furthermore, the prior art also teaches the use of control valves for controlling the gaseous discharge flow from the inflator. The inflation rate and capacity may be controlled responsive to the sensed or estimated severity of the crash, whereby a low severity would require a lower inflation rate or inflation capacity than a high severity crash. Since lower severity crashes are more likely than those of higher severity, and since such a controlled inflator would likely be less aggressive under lower severity crash conditions than those of higher severity, occupants at risk of injury by the air bag inflator because of their size or position will be less likely to be injured overall because they are more likely to be exposed to a less aggressive inflator. However, the risk of injury to such occupants would not be mitigated under the conditions of higher crash severity when the inflator is intentionally made aggressive in order to provide sufficient restraint for normally positioned occupants.
Ideally, the air bag would be inflated prior to any interaction with a normally seated occupant, and at a rate which is sufficiently slow that an out of position occupant would not be injured by the inflating air bag. For a crash of sufficient severity, this requires the crash sensing system to be able to predict immanent crashes because the time required to inflate the bag at an inflation rate that is sufficiently slow to be safe for out-of-position occupants may be greater than either that required for the occupant to move so as to commence interaction with an inflated air bag or to safely decelerate the occupant.
Current sensing technology uses accelerometers to detect the occurrence of the actual crash and therefore make it impossible to activate the safety devices prior to the crash. Radar sensors are currently being investigated for intelligent cruise control applications that merely provide a convenience to the operator of the vehicle in terms of maintaining a safe distance from other vehicles and slow the host vehicle by braking or throttling the engine. Failure of such a system will only inconvenience the driver and force them to maintain their own distance. Collision prediction sensors, however, must operate with 100 percent effectiveness since the passenger safety is at risk. In light of this the system must operate in a reliable and robust manner under all imaginable operating conditions and traffic scenarios.
Radar sensors are also currently being investigated for collision avoidance, where the host vehicle is radically slowed or steered away from the collision. However, these systems are not integrated into the deployment decision process of the safety restraint systems.
The disadvantage with existing post-crash detection systems derives from the fact that the time available to deploy an active safety device is very short, particularly for side impact or high speed frontal collisions where occupant restraint systems can provide significant safety benefits. These short time frames lead to rates of inflation of the airbags that are so great that injury or death are possible if the occupant is not well aligned with the airbag.
The disadvantage of proposed intelligent cruise control systems is that the field of view is only a few lane widths ahead of the vehicle (10-12 degrees maximum). These systems are thus incapable of detecting off-angle frontal or side impact crashes.
The disadvantage of the collision avoidance systems is that the control of the vehicle is taken from the driver to actively steer the vehicle to safety. This requires significant intelligence to detect a safe course of travel, which in turn increases the time needed for processing, and the overall cost of the system. Additionally, most collision avoidance systems only address the situation where the host vehicle is moving and will collide with another object. The issue of a stationary host and a target vehicle that is moving and responsible for the collision is not properly addressed.
For measuring objects closely spaced in angle, all systems have been relying on very narrow radar beamwidths that add further cost to the system, and can make the antenna undesirably large and difficult to install on a vehicle.
Generally, known automotive radar systems use range information to a target, and then estimate target speed using sequential range measurements to determine the change in distance over time. Such automotive radar systems use either a dual frequency ranging method, or continuous linear frequency modulated (FM) signals. The dual frequency method uses two tones to derive range from the relative phase between the two signals. The linear FM approach uses a continuously swept ramped waveform of increasing frequency with time. This is then repeated over and over.
The dual frequency method is useful for a single target within the radar beam for estimating the range. However, in a predictive collision sensing application, a radar needs to track multiple targets at varying ranges within a field of interest because each such target is a potential collision. For multiple targets, multiple ramps would be required, thereby creating the need for a very complicated radar system that can detect the various ramps and their resultant signals.